This invention relates to sheet metal squaring shears, and, more specifically, to improvements in the apparatus which drives the movable blade, the blade gap adjustment mechanism, a workpiece hold down device, and the manner in which the drive actuator is mounted to the apparatus. While the ensuing description is directed to the squaring or shearing of metal, the machine of the present invention may also be utilized in conjunction with the shearing of paper, cardboard, or even plastic.
One aspect of conventional metal working operations necessitates the squaring or shearing of metal sheets or plates, which may vary in thickness from a few thousandths of an inch to a half inch. The apparatus for performing this operation is conventionally called a squaring shear. In most sheet metal squaring shears, a fixed lower blade is secured to a bed. The metal sheet or other workpiece to be sheared is laid onto or fed over the bed, and a movable upper blade is mounted for reciprocation back and forth past the fixed lower blade. As the upper blade moves downwardly past the lower blade, it engages the metal sheet or workpiece to be sheared, and cuts the workpiece between the fixed blade and the vertically movable blade.
In several types of shears, the upper moving blade is mounted on a piece of apparatus called the ram, and the ram is slidably mounted between two tracks in opposed side brackets which are conventionally called gibs. Each gib is a support plate or bracket which is mounted to the side wall of the machine frame. Therefore, the movable blade extends between the side walls of the housing and reciprocates vertically along the tracks in which it is held.
Squaring shears are divided into two general types. Mechanical shears are of the type in which a continuously rotating electric motor turns a flywheel which operates through a gear box to turn a drive shaft. The advantages of such machines include a faster and thus cleaner cut, relatively high production (up to 60 cuts per minute), and minimum blade clearance adjustment. It has been found that the quicker the blade moves through the material, the cleaner the cut and the less the tendency of the material to bend or distort from side to side. On the Other hand, mechanical shears are relatively expensive in that they require more parts and many of the parts are expensive custom mechanical parts. Further, the mechanical shear must travel through the entire 360.degree. of the motor for each stroke and "short stroking" is not possible. Also adjustment of the blade clearance or "gap" is difficult.
The second type of shearing machines are the hydraulic shears. Such machines utilize one or more reciprocal linear hydraulic actuators to activate the upper blade relative to a fixed lower blade. Hydraulic shears are relatively simple as compared to mechanical shears and generally require fewer and less complicated parts than their mechanical counterpart. Thus the initial cost of hydraulic shears is less (approximately 75% as much as mechanical shears). Other advantages include the capability of "short stroking", rapid blade adjustment, and include inherent overload protection. However, there are distinct limitations to these machines. For example, the speed of the cut is much slower (approximately 15-18 strokes per minute). This results in a cut that is less clean, greater material distortion, and significantly less production. Adjustment of the blade clearance must occur more often.